Shannon L. Harris

Broad vaccine coverage predicted for a bivalent recombinant factor H binding protein based vaccine to prevent serogroup B meningococcal disease

Factor H binding proteins (fHBP), are bacterial surface proteins currently undergoing human clinical trials as candidate serogroup B Neisseria meningitidis (MnB) vaccines. fHBP protein sequences segregate into two distinct subfamilies, designated A and B. Here, we report the specificity and vaccine potential of mono- or bivalent fHBP-containing vaccines. A bivalent fHBP vaccine composed of a member of each subfamily elicited substantially broader bactericidal activity against MnB strains expressing heterologous fHBP than did either of the monovalent vaccines. Bivalent rabbit immune sera tested in serum bactericidal antibody assays (SBAs) against a diverse panel of MnB clinical isolates killed 87 of the 100 isolates. Bivalent human immune sera killed 36 of 45 MnB isolates tested in SBAs. Factors such as fHBP protein variant, PorA subtype, or MLST were not predictive of whether the MnB strain could be killed by rabbit or human immune sera. Instead, the best predictor for killing in the SBA was the level of in vitro surface expression of fHBP. The bivalent fHBP vaccine candidate induced immune sera that killed MnB isolates representing the major MLST complexes, prevalent PorA subtypes, and fHBP variants that span the breadth of the fHBP phylogenetic tree. Importantly, epidemiologically prevalent fHBP variants from both subfamilies were killed.

Safety, immunogenicity, and tolerability of meningococcal serogroup B bivalent recombinant lipoprotein 2086 vaccine in healthy adolescents: a randomised, single-blind, placebo-controlled, phase 2 trial

BACKGROUND Neisseria meningitidis serogroup B is a major cause of invasive meningococcal disease, but a broadly protective vaccine is not currently licensed. A bivalent recombinant factor H-binding protein vaccine (recombinant lipoprotein 2086) has been developed to provide broad coverage against diverse invasive meningococcus serogroup B strains. Our aim was to test the immune response of this vaccine. METHODS This randomised, placebo-controlled trial enrolled healthy adolescents from 25 sites in Australia, Poland, and Spain. Exclusion criteria were previous invasive meningococcal disease or serogroup B vaccination, previous adverse reaction or known hypersensitivity to the vaccine, any significant comorbidities, and immunosuppressive therapy or receipt of blood products in the past 6 months. Participants were randomly assigned with a computerised block randomisation scheme to receive ascending doses of vaccine (60, 120, or 200 μg) or placebo at 0, 2, and 6 months. Principal investigators, participants and their guardians, and laboratory personnel were masked to the allocation; dispensing staff were not. Immunogenicity was measured by serum bactericidal assays using human complement (hSBA) against eight diverse meningococcus serogroup B strains. The co-primary endpoints were seroconversion for the two indicator strains (PMB1745 and PMB17) analysed by the Clopper-Pearson method. Local and systemic reactions and adverse events were recorded. The study is registered at ClinicalTrials.gov, number NCT00808028. FINDINGS 539 participants were enrolled and 511 received all three study vaccinations--116 in the placebo group, 21 in the 60 μg group, 191 in the 120 μg group, and 183 in the 200 μg group. The proportion of participants responding with an hSBA titre equal to or greater than the lower limit of quantitation of the hSBA assays (reciprcocal titres of 7 to 18, depending on test strain) was similar for the two largest doses and ranged from 75·6 to 100·0% for the 120 μg dose and 67·9 to 99·0% for the 200 μg dose. Seroconversion for the PMB1745 reference strain was 17 of 19 (89·5%) participants for the 60 μg dose, 103 of 111 (92·8%) participants for the 120 μg dose, 94 of 100 (94·0%) participants for the 200 μg dose, and four of 73 (5·5%) participants for placebo. For the PMB17 reference strain seroconversion was 17 of 21 (81·0%) participants for the 60 μg dose, 97 of 112 (86·6%) participants for the 120 μg dose, 89 of 105 (84·8%) participants for the 200 μg dose, and one of 79 (1·3%) participants for placebo. The hSBA response was robust as shown by the high proportion of responders at hSBA titres up to 16. Mild-to-moderate injection site pain was the most common local reaction (50 occurrences with the 60 μg dose, 437 with the 120 μg dose, 464 with the 200 μg dose, and 54 with placebo). Systemic events, including fatigue and headache, were generally mild to moderate. Overall, adverse events were reported by 18 participants (81·8%) in the 60 μg group, 77 (38·9%) in the 120 μg group, 92 (47·2%) in the 200 μg group, and 54 (44·6%) in the placebo group. Fevers were rare and generally mild (one in the 60 μg group, 24 in the 120 μg group, 35 in the 200 μg group, and five in the placebo group; range, 0-6·3% after each dose). Incidence and severity of fever did not increase with subsequent vaccine dose within groups. One related serious adverse event that resolved without sequelae occurred after the third dose (200 μg). INTERPRETATION The bivalent recombinant lipoprotein 2086 vaccine is immunogenic and induces robust hSBA activity against diverse invasive meningococcus serogroup B disease strains and the vaccine is well tolerated. Recombinant lipoprotein 2086 vaccine is a promising candidate for broad protection against invasive meningococcus serogroup B disease. FUNDING Wyeth, Pfizer.

Detection of LP2086 on the cell surface of Neisseria meningitidis and its accessibility in the presence of serogroup B capsular polysaccharide

The outer membrane protein LP2086, a human factor H binding protein, is undergoing clinical trials as a vaccine against invasive serogroup B meningococcal (MnB) disease. As LP2086 is a surface protein, expression of capsular polysaccharide could potentially limit accessibility of anti-LP2086 antibodies to LP2086 expressed on the surface of bacteria. To determine whether variability in expression levels of the serogroup B capsule (Cap B) might interfere with accessibility of anti-LP2086 antibody binding to LP2086, we evaluated the ability of anti-Cap B and anti-LP2086 antibodies to bind to the surface of 1263 invasive clinical MnB strains by flow cytometry. One of the anti-LP2086 monoclonal antibodies used recognizes virtually all LP2086 sequence variants. Our results show no correlation between the amount of Cap B expressed and the binding of anti-LP2086 antibodies. Furthermore, the susceptibility of MnB bacteria to lysis by anti-LP2086 immune sera was independent of the level of Cap B expressed. The data presented in this paper demonstrates that Cap B does not interfere with the binding of antibodies to LP2086 expressed on the outer membrane of MnB clinical isolates.

Identification of an antigen-specific B cell population.

The difficulty in characterizing antigen-specific B cells that arise in the native B cell repertoire has been a formidable obstacle to understanding both protective and pathogenic antibody responses. We have developed a tetramer-based technique for identifying antigen-specific B cells. Biotin-labeled antigen is made tetrameric by interaction with streptavidin. The enhanced avidity of this antigenic compound for the B cell membrane permits the visualization, characterization and isolation of antigen-specific B cells.

Safety and immunogenicity of a meningococcal B bivalent rLP2086 vaccine in healthy toddlers aged 18-36 Months: a phase 1 randomized-controlled clinical trial

Background: A bivalent, recombinant, factor H–binding protein (rLP2086) vaccine was developed to protect against invasive Neisseria meningitidis serogroup B (MnB) in children and adolescents. Methods: Healthy toddlers (N = 99) were enrolled to 3 ascending dose-level cohorts (20, 60 or 200 &mgr;g). Within each cohort (n = 33), subjects were randomized to receive an initial formulation of the bivalent rLP2086 vaccine at 0, 1 and 6 months or hepatitis A vaccine/placebo control (2:1 ratio). Reactogenicity was assessed by parental reporting of local and systemic reactions using electronic diaries and reports of unsolicited adverse events. Immunogenicity was assessed by serum bactericidal activity assay using human complement and rLP2086-specific IgG binding. Results: The vaccine was considered to be well tolerated. Tenderness was the most frequently reported local reaction. Upper respiratory tract infection was the most commonly reported adverse event and occurred more frequently in the control group. Three cases (200 &mgr;g dose) of severe erythema that did not interfere with limb movement were reported. Four toddlers developed fever >40.0°C, 3 in the 200 &mgr;g group and 1 in the 60 &mgr;g group. Postdose 3, seroconversion (serum bactericidal activity assay using human complement ≥4-fold rise from baseline) was observed in 61.1–88.9% of participants against MnB strains expressing LP2086 variants homologous or nearly homologous to vaccine antigens and 11.1–44.4% against MnB strains expressing heterologous LP2086 variants. Seroconversion was observed in 77.8–100% of participants against additional, exploratory MnB strains expressing vaccine-homologous or heterologous LP2086 variants. Conclusions: This study shows that the bivalent rLP2086 vaccine is well tolerated and immunogenic in toddlers.

A phase 2 open-label safety and immunogenicity study of a meningococcal B bivalent rLP2086 vaccine in healthy adults

BACKGROUND Neisseria meningitidis serogroup B (MnB) is a leading cause of bacterial meningitis and septicemia in adolescents and young adults. No currently licensed and available vaccine has been shown to provide broad protection against endemic MnB disease. A bivalent rLP2086 vaccine based on two factor H-binding proteins (fHBPs) has been developed to provide broad protection against MnB disease-causing strains. METHODS This study assessed the safety and immunogenicity of the final formulation of a bivalent rLP2086 vaccine in 60 healthy adults (18-40 years of age) receiving 120 μg doses at 0, 1, and 6 months. Safety was assessed by collecting solicited reactogenicity data and participant-reporting of adverse events. Immunogenicity was evaluated by human serum bactericidal assay (hSBA) against 5 MnB strains expressing distinct fHBP variants and fHBP-specific immunoglobulin G titre. RESULTS After each immunisation, local reactions such as pain at the injection site and erythema were generally mild or moderate. The most common vaccine-related adverse event was upper respiratory tract infection, which was reported by two participants. Seroprotection (hSBA titres ≥ 1:4) was achieved in 94.3% of participants against a MnB strain expressing the vaccine-homologous fHBP variant A05 and 70.0%-94.7% against MnB strains expressing the heterologous fHBP variants B02, A22, B44, and B24. Seroconversion rates (≥ 4-fold rise in hSBA titres) ranged from 70.0% to 94.7% across the five MnB test strains following the 3-dose vaccination regimen. Immunogenicity responses tended to increase upon subsequent vaccine doses. CONCLUSIONS Bivalent rLP2086 is a promising vaccine candidate for broad protection against MnB disease-causing strains.

A randomized, controlled, phase 1/2 trial of a Neisseria meningitidis serogroup B bivalent rLP2086 vaccine in healthy children and adolescents.

Background: Neisseria meningitidis serogroup B (MnB) is a significant cause of invasive meningococcal disease. Factor H binding protein (also known as LP2086) is a conserved outer membrane neisserial lipoprotein that has emerged as a strong candidate protein antigen for MnB vaccination. This study examined the safety, tolerability and immunogenicity of an initial formulation of a bivalent recombinant LP2086 (rLP2086) vaccine in healthy children and adolescents. Methods: In this randomized, observer-blinded, parallel-group, multicenter trial conducted at 6 centers in Australia, 127 healthy participants aged 8–14 years were assigned to receive 20, 60 or 200 µg of the bivalent rLP2086 vaccine (n = 16, 45 and 45, respectively) or active control (Twinrix, n = 21) at 0, 1 and 6 months. Immunogenicity was assessed before the first dose and 1 month after doses 2 and 3. Local reactions, systemic events and other adverse events were recorded. The primary immunogenicity endpoint was the rate of seroconversion (≥4-fold rise in human complement serum bactericidal assay titer) against MnB strains expressing the homologous A05 or heterologous B02 LP2086 variants. Results: The bivalent rLP2086 vaccine was generally well-tolerated, with mostly mild to moderate local reactions. The most common adverse events, headache and upper respiratory tract infection, occurred with similar frequency in each group. Post-dose 3 seroconversion rates against strains expressing B02 and A05 variants were 68.8–95.3% for rLP2086 recipients and 0% for Twinrix recipients. Conclusions: The bivalent rLP2086 vaccine was well-tolerated and immunogenic in healthy children and adolescents, supporting further evaluation as a broadly protective MnB vaccine.

Highly Conserved Neisseria meningitidis Inner-Core Lipopolysaccharide Epitope Confers Protection against Experimental Meningococcal Bacteremia

Inner-core lipopolysaccharide (LPS) from Neisseria meningitidis is under investigation as a vaccine for prevention of meningococcal disease caused by N. meningitidis serogroup B (NmB). We investigated the functional activity of murine monoclonal antibody (MAb) B5 that recognizes a highly conserved (galE) LPS epitope. Three patterns of MAb reactivity were observed in N. meningitidis by Western blot, depending on the relative prevalence of sialylated, nonsialylated, and/or truncated LPS glycoforms. Three representative N. meningitidis strains (8047, M986, and 2996) were investigated with MAb B5 in functional assays in vitro and in vivo. MAb B5 completely protected infant rats against bacteremia caused by 8047, partially protected against 2996, and had no protective activity against M986. Thus, an inner-core LPS epitope can be a target for protective immunity, but the affinity of MAb B5 may only be sufficient to mediate protection against NmB strains possessing at least some truncated glycoforms.

The Discovery and Development of a Novel Vaccine to Protect against Neisseria meningitidis Serogroup B Disease

Vaccines have had a major impact on the reduction of many diseases globally. Vaccines targeted against invasive meningococcal disease (IMD) due to serogroups A, C, W, and Y are used to prevent these diseases. Until recently no vaccine had been identified that could confer broad protection against Neisseria meningitidis serogroup B (MnB). MnB causes IMD in the very young, adolescents and young adults and thus represents a significant unmet medical need. In this brief review, we describe the discovery and development of a vaccine that has the potential for broad protection against this devastating disease.

Preclinical evidence for the potential of a bivalent fHBP vaccine to prevent Neisseria meningitidis Serogroup C Disease

A bivalent factor H binding protein (fHBP) vaccine for the prevention of disease caused by Neisseria meningitidis serogroup B is currently in clinical development. Since fHBP is also expressed by other meningococcal serogroups, anti-fHBP antibodies may have bactericidal activity against meningococci independent of serogroup. To begin examining the susceptibility of other meningococcal serogroups to anti-fHBP antibodies, meningococcal serogroup C invasive isolates (n = 116) were collected from the Centers for Disease Control and Prevention’s Active Bacterial Core surveillance (ABCs) sites during 2000–2001. These isolates were analyzed for the presence of the fhbp gene. All serogroup C isolates contained the gene, and sequence analysis grouped the proteins into two subfamilies, A and B. Flow cytometry analysis demonstrated that fHBP was expressed on the surface of ~70% of isolates in vitro with varying levels of expression. fHBP was accessible to antibodies on the cell surface even in the presence of the polysaccharide capsule. Nine isolates from different geographic regions were identified which harboured an identical single nucleotide deletion that could result in a truncated subfamily B fHBP. Analysis by flow cytometry using a polyclonal fHBP antibody preparation revealed that a subpopulation of each of these isolates expressed fHBP. Rabbit and non-human primate immune sera generated with bivalent fHBP vaccine were tested for bactericidal activity against a panel of diverse serogroup C clinical isolates using human complement. Sera from both species demonstrated serum bactericidal antibody activity against the serogroup C isolates tested. These promising findings suggest that a bivalent fHBP vaccine may be capable of providing protection against meningococcal disease caused by both serogroup C and B.